The long-term goal of this project is to identify novel monoclonal antibodies (mAbs) that broadly recognize the HIV-1 envelope glycoprotein (Env) and block infection in vitro to guide vaccine development. This goal will be pursued in local cohorts of HIV-1 infected individuals who control their infections in the absence of anti-retroviral therapy (JAIDS, 50:403-8, 2009). Approximately 13% of these individuals have circulating broadly neutralizing antibodies providing the study population for our studies. A key element of our approach is the development of a new assay to census Env-specific memory B cell clones (BMem) that allows the rapid and direct cloning of full-length molecular clones of the antibodies expressed by these cells (PNAS, 106:3952-7, 2009). This method permits clone identification using native oligomeric HIV-1 envelope glycoproteins (Env) expressed on cell surfaces and by direct neutralization of pseudoviruses. Env-reactive clones are used to produce mAbs that will be evaluated for epitope specificity and neutralization breadth. This information will be used to test the hypothesis that neutralization breadth is determined by monoclonal or pauciclonal responses comprised of one or a very few neutralizing specificities as opposed to a polyclonal response comprised of a mosaic of neutralizing specificities. There are two specific aims. Aim 1- To develop clonal specificity profiles of Env-specific BMem from NVS who have ongoing broadly neutralizing antibody responses- Clonal specificity profiles of anti-Env responses will be determined by limiting dilution analysis, mAb isolation, and epitope mapping to identify broadly neutralizing mAbs. Aim-2- To compare neutralization breadth between plasma antibodies and mAbs representing a full clonal profile of BMem to determine the number of mAbs that must be pooled to reconstruct the neutralization profile of the circulating antibody pool. Neutralization breadth of mAbs will be determined using standardized pseudovirus assays. This data will be used to determine the clonality of an ongoing broadly neutralizing antibody response. This aim will test the hypothesis that neutralization breadth is determined by monoclonal or pauciclonal responses comprised of one or a very few neutralizing specificities as opposed to a polyclonal response comprised of a mosaic of neutralizing specificities. PUBLIC HEALTH RELEVANCE: This research is relevant to public health in that it seeks to understand how people who are infected with the AIDS virus make protective immune responses. This information will help guide the development of a vaccine against the AIDS virus.